Lead-in shield



Nov. 18, 1941. w POWER 2,263,396

LEAD- IN SHIELD Filed June 25, 1938 MuB vum A I I INVENIOR. DONNELL n4 POWER BY c Efl ATTORNEY.

Patented Nov. 18, 1941 Donnell W. Power, Summit, N. mesne assignments, to Radio America, New York, N.

Delaware 1., assignor, by Corporation of Y., a corporation of Application June 25, 1938, Serial No. 215,722

6 Claims.

Myinvention relates to electron discharge devices, particularly to electrostatic shielding means between lead wires and base contact pins energized by high frequency current.

In th manufacture of high frequency electron tubes it has been accepted practice to seal the control grid lead and the anode lead in opposite ends of the envelope to separate the leads as much as possible and prevent excessive coupling and feedback at high frequency between the output and input electrodes and circuits of the tube. This practice'complicates tube manufacture and materially increases the cost of assembly, and receiver sets with circuit connections to the top of amplifier tubes are particularly expensive to manufacture.

An object of my invention is an electron discharge device for amplifying or generating high frequency waves constructed with control grid and anode leads and contact pins in one end of the tube and with novel shielding means for minimizing coupling between the leads and contact pins.

The characteristic features of my invention are defined with particularity in the appended claims and preferred embodiment are described in the following specification and shown in the accompanying drawing in which- Figure l is a sectioned perspective view of the preferred embodiment of my invention, and

Figures 2 and 3 show details of shielded tubes constructed according to my invention.

The tube shown in Figure 1 comprises a conventional metal shell i closed at its lower end with a header 2 having a metal ring 3, U-shaped in cross section with an outwardly extending flange 4 welded to the flange 4' on the shell. The inner leg of the U is sealed gas-tight to the periphery of a fiat disc-like press 5 of glass. Anode 6, screen grid 1, control grid 8, and cathode 9 containing a heater and exteriorly coated with an electron emissive material such as barium-strontium oxide, are held at their ends by side rods in insulating spacers and are joined to the lead wires in the press. Control grid 8 is connected to lead wire i0 and anode 6 is connected to lead wire l2, which is sealed in the press diametrically opposite the control grid lead wire. Lead wires ill and I2 are joined at their lower ends, as by soldering, to contact pins l3 and M, respectively, staked in insulating base plate I5. The base plate is attached at its periphery to a flanged skirt i8 welded to the header flange i. A hollow locating lug or centering pin ll, preferably integral with base plate, as dethe plate with a key scribed in the United States patent to T. M. Shrader 2,080,837, extends from the center of I8 along one side slightly longer than the contact pins, to rotationally. orient the base in socket.

Contrary to the usual practice of providing a continuous metal partition between metal elements to be shielded, I have found that the control grid lead-in conductor Ill and its pin l3 may be effectively isolated from the plate lead conductor l2 and its pin H by a simple rod-like or tubular shield extending along the axis of the tube from the ends of the pins to the electrodes. The exhaust tube IS in the center of the press and the locating lug may conveniently be employed to position and hold the shield in place. The shield comprises two metal sections, one surrounding the exhaust tube exteriorly of the envelope and a second inserted in the upper end of the exhaust tube interiorly of the envelope. The first is a metal sleeve fitted inside the 10- cating lug connected by an ear 2! to grounding pin 22, and the other is a conical or funnelshaped metal piece 23, longer than the thickness of the press, inserted-in the upper end of the exhaust tube and joined by an ear extension 24 to the lead-in conductor 25 of the grounding pin. The upper end of the grounding conductor is preferably connected to the metal envelope. A getter heating coil may conveniently Join the conductor and envelope. The lower end of the metal cone 23 extends downwardly in the exhaust tube and as near as practical to the upper end of the metal sleeve 20. Shield 20 may, if desired, be stamped from sheet metal and rolled into a cylinder with an open slit along one side and with a radial fin integral with one edge of the slit for attachment to the ground pin. The cylinder preferably is slightly larger than the inside of the lug so that the cylinder can be compressed and slid into the lug with yielding slid fit. I have found that these two metal pieces connected together and to ground so effectively neutralize electrostatic coupling between control grid and anode lead-in conductors and pins, that at even ultra-high frequencies, such as megacycles per second, the energy transfer between control grid and anode leads is insufllcient to cause troublesome feedback. The capacitance between wires in the press caused by the high dielectric constant of the press material is efi'ectively minimized by the exhaust tube insert 28 extending through the press.

While I am not certain why my shielding arrangement is so effective in preventing interdiifers from the conventional procedure of assemebctrode eoupling,.it is my belief that many of the electrostatic lines of force emanating from the anode lead and pin are intercepted by the shielding members 2l'and 23. The remaining lines deflected toward the other electrode lead-in s conductors and pins, such as those connected to the screen grid, cathode and heater, which are usually maintained at zero radio frequency potential are intercepted and passedto ground. Because of the intercepting and grounding action 1 of the center shields 2! and 22 and the intermediate leads and pins, the necessity for a continuous metal partition between the control grid and anode leads is obviated. The usual high interlead capacitance in the press caused by the high dielectric constant of glass is effectively minimised by my novel shield in the exhaust tube.

The metal sleeve 2| may conveniently be replaced by a continuous metal coating 28 as shown in Figure 2. A ilne metal spray such as powdered copper or iron mixed with a liquid vehicle such as carbon tetrachloride may be painted or sprayed on the inner surface of the locating lug and a strip of this spray continued from the rim of the lug to the grounding pin 22. A mask placed over the base exposing only the interior of the centering lug, the end of pin 22,

and a narrow path between the pin and lug facilitates application by spraying of the metal coating material.

Alternatively, the locating lug 21 may be drawn from relatively heavy sheet metal and staked at its upper end, as shown in Figure 3, in the insulating disc orwafer 28 carrying the contact pins. The wafer is clamped along its periphery to the depending skirt 29 joined to the flange of the metal shell. The metal locating lug is electrically connected to the grounding pin 22.

It can be seen that a conventional receiver tube of the metal envelop type with a flat press and a conventional base having contact pins arranged in a circle around a hollow locating lug in the center of the base can be easily shielded to eliminate the troublesome top cap. The 10- cating lug is telescoped over the exhaust tube extending from the center of a flat disc-like press, and a tubular shield is fitted in the locating lug and around the exhaust tube and connected at its upper end to a grounding pin without alterlng the design of the tube. The lead wire of this pin passed through the press and con- .nected to the metal envelope and to a conical metal shield fitted in the upper end of the exhaust tube, completes the shielding.

In manufacture metal cone 2! is inserted in the end of the exhaust tube and its ear attached to conductor 25 and the electrodes are assembling metal tubes only by the insertion of the metal piece 22 and the insertion of sleeve 20. Figure 1, addition of spray 26, Figure 2, or substitution of metal lug 21, Figure 3. The addition of these two shielding .pieces obviates the end of said envelope, an exhausttube extending outwardly from the center of said press, an

and pins connected to said conductors in opposite sides of said plate, a locating lug centrally in said plate telescoped over said exhaust tube, and means for electrostatically isolating said conductors and pins comprising a metal shield with a tubular portion surrounding said exhaust tube and a metal insert in said exhaust tube, said insert and tubular portion being connected to a third contact pin and to the envelope.

2. An electron discharge device comprising an envelope containing a cathode, a control grid and anode, a flat disc-like glass press closing one end of said envelope, a plurality of circularly arranged conductors insulatingly sealed in said press, an exhaust tube extending outwardly from the center of said press, an insulating base secured to said envelope in parallel spaced relation to said press, spaced conductors being connected to said control grid and to said anode, and connected to spaced pins in said base, a locating lug extending from the center of said plate and telescoped over said exhaust tube, and means for electrostatically isolating said conductors and pins comprising a tubular metal shield surrounding said exhaust tube in the locating lug and a metal, shielding member inserted in the upper end of said exhaust tube, said tubular shield and member being connected together. e

3. 'An electron discharge device comprising an envelope containing a cathode, a control grid and anode, a flat disc-like press closing one end of said envelope, an exhaust tube extending outwardly from the center of said press, an insulating base plate secured to said envelope in parallel spaced relation to said press, conductors connected to said control grid and said anode sealed in said press on opposite sides of said exhaust tube, and pins connected to said conductors in opposite sides of said plate, a hollow locating lug integral with said plate telescoped over said exhaust tube and means for electrostatically iso-- lating said conductors and pins comprising a metal coating on the interior surface of said lug surrounding said exhaust tube and a metal insert in the upper end of said exhaust tube, said coating and said insert being connected to' a common contact pin.

4. An electron discharge device comprising an envelope containing cooperating electrodes including a control grid and anode, a flat disc-like Dress closing one end of said envelope, an exhaust tube extending outwardly from the center of said press, an insulating base plate secured to control grid lead-in said envelope in parallel spaced relation to said Dress, spaced conductors connected to said control grid and said anode sealed in said press, and parallel spaced contact pins connected to said conductors supported by said plate, means for electrostatically isolating said conductors and pins comprising a tubular metal locatlnglug centrally between said pins and joined at its upper end to said plate, a metal insert in the upper end of said exhaust tube, said insert and lug being connected to a third contact pin.

5. An electron tube for high frequency signalling systems comprising an electrode assembly, an enclosing envelope for said assembly consisting of a bulb portion sealed at its lower end in a vacuum-tight manner to a non-reentrant glass header flattened in a plane substantially transverse to the longitudinal axis of the tube and having an exhaust opening, an exhaust tubulation depending irom said header in alignment 20 with said opening, a plurality oi lead-in members sealed through said header and disposed around said tubulation, an electrostatic shielding member extending downward and into said exhaust tubulation and connected to one or said lead-in members.

6. An electron tube for high frequency signalling systems comprising an electrode assembly, an enclosing envelope for said assembly consisting of a bulb sealed in a vacuum-tight manner at its lower end to a non-reentrant glass header, an exhaust tubulation downwardly depending from said header, a plurality oi lead-in members sealed through said header around said tubulation, and electrostatic shielding means consisting of a metal member extending downwardly into said exhaust tubulation and substantially through said header, and another metal member exteriorly surrounding said tubulation, both said metal members being electrically connected to one of said lead-in members.

DONNELL W. POWER. 

